Peripheral Nervous System Flashcards
peripheral nervous system (PNS)
-composed of the afferent and efferent fibers that relay signals between the CNS and the periphery (other parts of the body)
afferent division
detects, encodes and transmits the peripheral signals to the CNS
sensory receptors
- specialized peripheral ending of afferent neurons
- each type responds to its one adequate stimulus
- translates the energy form of the stimulus into electrical signals
- process is called signal transduction
- very specific
sensory transduction
- the conversion of stimulus energy into a receptor potential
- receptor potentials in turn trigger action potentials in the afferent fiber
adequate stimulus
-each type of receptor is specialized to respond to one type of stimulus
photoreceptors
responsive to visible wavelengths of light
mechanoreceptors
- sensitive to mechanical energy
- skin, eardrum, muscles
thermoreceptors
sensitive to heat and cold
osmoreceptors
-detect changes in solute concentrations in body fluids and resultant in osmotic activity
chemoreceptors
- sensitive to specific chemicals
- taste and smell
- detect O2 and CO2 in blood
- detect chemical content of digestive tract
- pH and the concentration of H ions
nociceptors
- pain receptors
- sensitive to tissue damage or distortion of tissue
information detected by receptors
- regulating motor behavior in accordance with external circumstances
- coordinating internal activities directed at maintaining homeostasis
- cortical arousal and consciousness
- perceptions of the world around us
- changing emotional states
receptor potentials
- a graded, depolarizing receptor potential promoting net Na+ entry
- if strong enough will generate action potentials
- move along afferent fibers to the CNS
- the strength of the stimulus determines the frequency of action potentials
receptor adaptation
- may adapt slowly or rapidly to sustained stimulation
- may be tonic or phasic receptors
tonic receptors
- do not adapt at all or adapt slowly
- useful when it is valuable to maintain information about a stimulus
- muscle stretch receptors
phasic receptors
- rapidly adapting receptors
- useful when it is important to signal a change in stimulus intensity rather than delay the information
receptive fields
- an area surrounding a receptor within which the receptor can detect stimuli
- the acuity (to distinguish) of a body region varies inversely with the size of the receptive fields
- smaller receptive fields show higher acuity
- also influenced by lateral inhibition
hair receptor
- rapidly adapting
- senses hair movement and very gentle touch
Merkel’s disc
- slowly adapting
- detects light
- sustained touch and texture
pacinian corpuscle
- rapidly adapting
- responds to vibration and deep pressure
ruffini endings
- slowly adapting
- respond to deep, sustained pressure and stretch of the skin
Meissner’s corpuscle
- rapidly adapting
- sensitive to light, fluttering touch
perception
- the conscious interpretation of the external world
- what the brain perceives from its input is an abstraction and not reality
- the only stimuli that can be detected are those for which receptors are present
pain
- primarily a protective mechanism to bring aware that tissue damage is occurring
- starts with nociceptors
- sensation of pain is accompanied by behavioral responses and emotional reactions
- can be influenced by past or previous experiences
- mechanical, thermal and polymodal
polymodal
-receptors respond to multiple pain stimuli
pain pathway
- afferent pain fibers terminate in the spinal cord
- ascending pathways that transmit the signal to the brain
- substance P is the spinal cord pain neurotransmitter
- descending pathways use endogenous opiates to suppress the release of substance P
- descending pathways serve as built in analgesic system
afferent pain pathways
- fast: myelinated, sharp, prickling pain signals
- slow carries dull, aching, persistent pain signals
eye
- sensory organ for vision
- three layers: sclera/cornea, choroid/ciliary body/iris, retina
sclera
- tough outer layer of connective tissue
- forms visible white part of eye
cornea
- anterior, transparent outer layer
- light rays pass through it before entering interior of eye
choroid
- middle layer underneath sclera, contains blood vessels that nourish retina
- forms ciliary body and iris
ciliary body
controls lens shape
iris
controls the amount of light entering the eye
pupil
- opening through which light enters the eye
- size is adjusted by the iris muscle
blind spot
area with no rods or cones (photoreceptors)
retina
- innermost coat under choroid
- consists of inner nervous-tissue layer and outer pigmented layer
- rods and cones: light detecting photoreceptors in the nervous tissue layer
- pigmented layer absorbs light after it passes by the rods and cones
refraction of light
- the bending of a light ray
- convex: converge light rays
- concave: diverge light rays
- changes in different media
cornea and lens
- primary refractive structures that bend incoming light rays
- cornea contributes most of the total refractive ability of the eye
- strength of lens can be adjusted to accommodate for differences in near and far vision
eye accommodation
- ability to adjust strength of lens by changing its shape
- shape is regulated by ciliary muscle
presbyopia
-age related reduction in accommodation ability
myopia
nearsightedness
hyperopia
farsightedness
neural retina
- contains 3 layers of excitable cell
- outermost: rods and cones (absorb light)
- middle: bipolar cells
- inner: ganglion (axons join to form the optic nerve)
optic disc
- point of retina where the optic nerve leaves
- called bling spot
- no image can be detected
fovea
- small depression in center of retina
- has only cones
- no bipolar or ganglion cells
- point of most distinct vision
macula lutea
- area immediately surround fovea
- has cones, bipolar and ganglion cells
- fairly high acuity
photopigment
- opsin: integral protein in the plasma membrane
- retinal: a derivative of vitamin A that absorbs light (carrots)
rhodopsin
- photopigment in rods
- in the dark, inactivated, cis conformation
- in the light, activated, trans conformation
phototransuction
- process of converting light stimuli into electrical signals
- activation of the photopigment by light causes a receptor potential in the rod or cone which can lead to action potentials in ganglion cells
visual pathways
- right brain receives information from the left field of view of each eye and vise versa
- cross at the optic chiasm
ear contains three parts
external, middle and inner
external and middle ear
-transmit and amplify airborne sound waves to the fluid filled inner ear
inner ear
- contains neural receptors cells for 2 sensory systems:
- cochlea: hearing
- vestibular: apparatus for equilibrium
sound waves
-traveling vibration of the air
pitch or tone
-determined by the frequency of vibrations
intensity or loudness
-depends on the amplitude of the sound waves
hearing involves two aspects:
- identification of the sound, “what”
- localization of the sounds “where”
timbre or quality
- depends on the overtones
- additional frequencies superimposed on the fundamental pitch/tone
sound transduction
- waves enter through the external ear
- tympanic membrane vibrates with sound waves
- middle ear converts tympanic membrane vibrations into fluid movements in cochlea
- the organ of corti (sense organ for hearing) rests on the basilar membrane in cochlea
- movement of fluid in inner ear causes the basilar membrane to vibrate
- cilia on hairs are bent
- the bending of cilia transduces sound waves into electrical signals
role of stereocilia in transduction
- tips link stretch and open channels when the stereocilia bend towards the tallest member
- more K+ enters
- cell depolarizes
- opens Ca2+ voltage gated channels
- Ca2+ entry cause a greater release of the neurotransmitter
- more transmitters leads to a higher rate of action potentials
pitch discrimination
-depends on region of the basilar membrane that vibrates
loudness discrimination
-depends on the amplitude of vibration of the basilar membrane
auditory cortex
- primary: in the temporal lobe, tonotopically organized
- each region of the basilar membrane is connected to a specific region
- specific cortical neurons are activated only by particular tones
- higher-order auditory cortex- integrates the separate sounds into a meaningful pattern
vestibular apparatus
-consists of semicircular canals and otolith organs
equilibrium
-sense of body orientation and motion
semicircular canals
-detect rotational or angular acceleration or deceleration of the head
otolith organs
- detect changes in the rate of linear movement
- provide info about head position relative to gravity
production of receptor potential in hair cells
- hair depolarizes when stereocilia are bent towards the kinocilium
- hair hyperpolarizes when stereocilia are bent away from kinocilium
equilibrium transduction
- neural signals are generated as fluid moves within vestibular sense organs
- mechanical deformation of hair cells occurs in response
- the bending either depolarizes or hyperpolarizes receptor potentials
otoliths
- crystals of CaCO3
- calcium carbonate
vestibular projections
- signals from the vestibular apparatus are carried through the vestibulocochlear nerve to the vestibular neclei
- maintains balance, posture, eye movement, perceiving motion and orientation
chemoreceptors
-detect taste and smell
taste receptors
-found in taste buds on tongue
olfactory receptors
-located in the olfactory epithelium in the nasal cavity
taste and smell senses
- dissolved molecules bind to site on the receptor membrane
- binding causes receptor molecules which lead to action potentials
- continuously renewed
- route 1: to cortex for conscious perception
- route 2: limbic system for emotional and behavioral processing
taste bud
- small opening: taste pore
- fluid in mouth enter pore and come into contact with receptor cell
taste receptor cells
-modified epithelial cells with microvilli
tastants
- plasma membrane of microvilli contains receptors for specific chemical signals
- binding causes receptor to induce electrical signals in cell
primary tastes
- salt: chemical salts
- sour: acids
- sweet: configuration of glucose
- bitter: diverse group of tastants
- umami: savory taste triggered by animo acids
olfactory mucosa 3 cells
- olfactory receptor neurons
- supporting cells
- basal cells
olfactory receptor neurons
- primary sensory neuron
- dendrite exposed at surface of mucosa
- dendrite contains cilia where odorant molecules bind
- axons of receptors cells collectively form olfactory nerve
supporting cells (olfactory)
-secrete mucus to help odorant molecules interact with receptor sites
basal cells (olfactory)
- precursors of new olfactory receptor cells
- as olfactory nerves degenerate, basal cells divide to give rise to new receptor cells
olfactory bulb
- axons from the olfactory neurons
- synapse onto mitral cells (output cells of bulb)
- synapse takes place in the glomerulus
- axons from the mitral cells from the olfactory tract and project to the limbic system and cerebral cortex
